An artery is one of the tube-shaped blood vessels that carry blood away from a heart to the body's tissues and organs. An artery is made up of an outer fibrous layer, a smooth muscle layer, connecting tissues and inner lining cells. If arterial walls become hardened due to the accumulation of fatty substances, then blood flow can be diminished. Hardening of the arteries, or loss of vessel elasticity, are termed arteriosclerosis while fatty deposit build-up is termed atherosclerosis. Atherosclerosis and its complications are a major cause of death in the United States. Heart and brain diseases are often the direct result of this accumulation of fatty substances that impair the arteries' ability to nourish vital body organs.
Balloon angioplasty is a nonsurgical method of clearing coronary and other arteries, blocked by atherosclerotic plaque, fibrous and fatty deposits on the walls of arteries. A catheter with a balloon-like tip is threaded up from the arm or groin through an artery until it reaches the blocked area. The balloon is then inflated, flattening the plaque and increasing the diameter of the blood vessel opening. The arterial passage is thus widened. As a result of enlarging the hardened plaque, cracks may unfortunately occur within the plaque to expose the underlying fresh tissue or cells to the blood stream.
There are limitations, however, to this technique's application, depending on the extent of the disease, the blood flow through the artery, and the part of the anatomy and the particular vessels involved. Plaque build-up and/or severe re-stenosis recurs within 6 months is up to 30-40 percent of those treated. Balloon angioplasty can only be characterized as a moderate-success procedure. Recently, a newer technique of inserting a metallic stenting element is used to permanently maintain the walls of the vessel treated at its extended opening state. Vascular stents are tiny mesh or coil tubes made of stainless steel or other metals and are used by heart surgeons to prop open the weak inner walls of diseased arteries. They are often used in conjunction with balloon angioplasty to prevent restenosis after the clogged arteries are treated. Stenting technique reduces the probability of restenosis; however, the success rate is still sub-optimal. The underlying fresh tissue or cells still pose as a precursor for vessel reclosures or angio-spasm.
Atherectomy is a relatively newer technique developed for opening the lumen of an occluded vessel, and like the balloon angioplasty technique, provides an alternative to the traditional coronary bypass surgery. Atherectomy involves physically breaking up the material that blocks or partially blocks the vessel. Several types of atherectomy devices have been developed. U.S. Pat. No. 4,445,509, No. 4,895,560, No. 4,966,604, No. 4,990,134, No. 5,217,474, No. 5,766,192, No. 5,779,722, No. 5,836,957, and No. 5,843,103 incorporated herein by reference, disclose a rotatable abrasive surface that is introduced into the obstructed vessel. At the obstruction the abrasive surface is rotated at a high rate of speed to abrade or cut away at the obstruction.
One major drawback with rotatable abrasive atherectomy devices is that they open up the plaque or the obstruction and expose the underlying collagen or damaged endothelium to the blood flow. Fresh collagen has pro-thrombotic and platelet-affinity properties that are part of body's healing process. Unless the collagen or the damaged endothelium is passivated or modulated, the chances for blood vessel clotting as well as restenosis exist. Moderate focal heat is known to tighten and shrink the collagen tissue as illustrated in U.S. Pat. No. 5,456,662 and U.S. Pat. No. 5,546,954. It is also clinically verified that thermal energy is capable of denaturing the tissue and modulating the collagenous molecules in such a way that treated tissue becomes more resilient ("The Next Wave in Minimally Invasive Surgery" MD&DI pp. 36-44, August 1998). Therefore, it becomes imperative to post-treat vessels walls after the walls are treated with angioplasty, stenting, or atherectomy procedures.
One method of reducing the size of cellular tissues in situ has been used in the treatment of many diseases, or as an adjunct to surgical removal procedures. This method applies appropriate heat to the tissues, and causes them to shrink and tighten. It can be performed on a minimal invasive fashion, which is often less traumatic than surgical procedures and may be the only alternative method, wherein other procedures are unsafe or ineffective. Ablative treatment apparatus have an advantage because of the use of a therapeutic energy that is rapidly dissipated and reduced to a non-destructive level by conduction and convection, to other natural processes.
RF therapeutic protocol has been proven to be highly effective when used by electrophysiologists for the treatment of tachycardia; by neurosurgeons for the treatment of Parkinson's disease; and by neurosurgeons and anesthetists for other RF procedures such as Gasserian ganglionectomy for trigeminal neuralgia and percutaneous cervical cordotomy for intractable pains. Radiofrequency treatment, which exposes a patient to minimal side effects and risks, is generally performed after first locating the tissue sites for treatment. Radiofrequency energy, when coupled with a temperature control mechanism, can be supplied precisely to the apparatus-to-tissues contact site to obtain the desired temperature for treating a tissue.
Other situations may arise where it is advantageous or desirable to combine the benefits of a rotatable atherectomy-like procedure with means for expanding the constricted vessel and a RF current therapy for providing focal thermal energy to the treated tissue. With the prior art devices presently available, it is necessary that an angioplasty, atherectomy, or stenting be performed first; then RF energy is applied. There is an urgent clinical need to shorten and simplify the procedure by simultaneously performing rotating procedure comprising RF energy therapy as part of the angioplasty, atherectomy or stenting procedures.
A stent deployed within a vessel or a rotatable metallic device has excellent metal-to-tissue contact surface. It becomes an ideal medium for applying appropriate thermal energy to the tissue needed for treatment or modulation. A metallic stenting element or a rotatable metallic device is useful in this case to shrink and tighten the target tissue. Therefore, there is a need for an improved medical apparatus having the capability to effectively contact the inner walls of a tubular vessel using radiofrequency energy to treat a vessel or other tissues, such as esophagus, larynx, uterus, urethra and the like.